Darton Engine Sleeves - Block Party

How To Get Big-Block Displacement In A Small-Block Package

The old saying, "There's no replacement for displacement," is dead-on accurate. Sure, you can stuff a big, nasty camshaft into a smaller engine, or spin that same engine into the rpm stratosphere and make more power, but extra cubes yields something that real performance junkies find more beneficial: torque. When it comes to going fast, torque is king and it's one reason why old-school big-block Chevy engines still command respect. Of course, the down side to all that big-block goodness is weight. It's a give-and-take deal; at least it used to be. Today it's possible to get crazy displacement even in the diminutive small-block package. For example, GM's line of lightweight aluminum LS engines started out at around 350 cubic inches. As time passed, that displacement steadily grew to 364, 376, and eventually topped out at 427 glorious inches in the LS7. But the power-mad masses clamored for more. The problem was that the iron-sleeved aluminum blocks could only be punched out so far before getting dangerously thin in the cylinder wall department. Of course there was the stroke side of the displacement calculation, but the factory sleeves were only so long. The solution turned out to be ditching the GM sleeves and going aftermarket.

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Now, this isn't something you're going to be able to do yourself using common hand tools in your garage. It involves very specialized and expensive equipment, but more importantly it requires someone with the skill and experience to pull off the surgery. That's where Steve Demirjian, of Race Engine Development, comes in. He's been in the racing engine business since 1972, and that equates to a lot of knowledge of what works and what doesn't. In regards to sleeves, he's been working with Darton for quite some time and is even one of the patent holders for their Modular Integrated Deck (MID) sleeve system. In other words, he was the perfect guy to help us up the displacement of our LS engine. The MID system was developed by Darton to address the factory blocks design weakness of cylinder stability due to the poor support at the upper deck area. GM's "cast in sleeves" makes the factory engines affordable, and they are great to a certain power level, but lacking when it comes to high power, boosted, or, as in our case, larger bore sizes. When the Darton sleeves are siamesed and nested they create a solid deck of sleeve flanges held in tension. This reinforces the upper deck area and provides for individual replacement with what Darton calls Modular Integrated Deck (MID). Also, this design enhances water flow from block to head and promotes stability of cooling since all the sleeves are of the "wet" design. Unlike factory sleeves, water flows all the way around the cylinders, which promotes cooling and helps control detonation. You can find more tasty tidbits about Darton's MID sleeves by hitting up their website.

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Darton Engine Sleeves - Block Party

This is how Darton receives the ductile iron sleeves from the foundry. At this point it can become any number of sleeves from LS applications, to sleeves for Pro Stock and Funny Car engines. The sleeve's job is to control wear, heat, provide a platform for lubricity, and contain the combustion process without distortion. Cast iron is typically very inexpensive, breaks in well, and is brittle. The opposite of ductile iron, which is more expensive, very strong, has high elongation (meaning flexibility without breaking), and high surface hardness. Ductile is composed of a nodular structure as opposed to cast iron, which has a more graphite-flake structure.

The ductile iron sleeve is then machined and phosphate coated to protect against rust and corrosion. At this point all of the LS sleeves are the same.

The result is this LS sleeve kit. While there are eight sleeves, there are actually three part numbers here. The four in the center, cylinder one and eight, and cylinders number two and seven.

The coated sleeves are placed into the CNC mill for all the detail cutting and drilling. The sleeves for LS1 engines (Gen III) come in two bore size ranges. The smaller set covers from 4.125 to 4.160 inches, while the lager goes from 4.170 to 4.200 inches. For the Gen IV blocks, there's just one part number that covers from 4.125 to 4.200 inches.

For this install, we found a used LS2 block that had a couple of gouged factory sleeves. We made sure that block didn't have any cracks or other damage. This one set us back $400, which is almost $1000 cheaper than new from GM. Used LS1 blocks can be found for even cheaper.

After changing cutting heads, Steve then removed the rest of the cylinder material. Even though a lot of material is removed, the new sleeves are thicker and an MID-sleeved block will end up about six pounds heavier than a stock LS block.

The block is then set up on the CNC for final machining for fitment of the sleeves. The sleeve diameters are measured for size with a micrometer then numbered and the block is machined per sleeve for correct fitment. The sleeves will vary slightly in diameter so one must measure the sleeves prior to doing the finish bore work in the block.

The first thing Steve Demirjian, of Race Engine Development, did after getting the block onto his mill was to plot all the distances. To say this is precision work is an understatement.

After this pass, we were left with aluminum bores. "On the smaller bore Gen III and Gen IV LS2 blocks, I cut a honing clearance bore slightly larger than 4.200 inches to just above the main webbing. That leaves sufficient clearance to enable honing of the blocks to 4.200 inches if desired, without crashing the honing stones into the block," remarked Steve.

As you can see, quite a bit of material is removed in this process. It's also easy to see how someone inexperienced with this process could end up junking a perfectly good block.

Time to start removing material. The first pass of the mill cuts out the GM iron cylinder liners. According to Steve, "All machining must be done on a flood coolant machine or else the heat buildup during machining will distort and expand the block. This will make the tolerances impossible to hold and put stress into the block so that it will distort even further when the engine is started."

With the rough cuts done, Steve then stress-relieved the block. "This is a critical step that most shops do not do, or know about, for that matter. No stress relief and the block will distort in service, leaving bores that are four to five thousandths out of round. The same is true (but to a lesser extent) with the dry-liner installs. In any event, I have a Formula 62 stress relief machine which relieves the block at its natural resonant frequency. As far as I am concerned, this is the best stress relief machine on the market and is used by thousands of high-tech companies including Boeing and GM. I leave the block on the machine for an hour to reduce internal stresses from machining to a minimum," said Steve.

And here's the reason why cylinder one has a specific sleeve. The sleeve is cut with an angular flat to prevent breakthrough into the timing cover area. The block is machined to the exact mirror image of that sleeve flat.

And here's the reason why cylinder one has a specific sleeve. The sleeve is cut with an angular flat to prevent breakthrough into the timing cover area. The block is machined to the exact mirror image of that sleeve flat.

For an extra 75 bucks, Steve can also notch the cylinders to clear the rod bolts. Considering how hard the ductile iron is, we were more than happy to have him knock out the notches.

With the machining done, the block was deburred, washed, and blown dry. Before dropping in the sleeves, Steve gave the lower cylinders a light coat of Molykote O-ring lubricant. The tolerances are tight, and this helps the sleeves slide into place without damage.

We then used a dead blow mallet to carefully seat the sleeves into the block. Steve also gave us some advice on eventually installing the heads. He stated, "If using other than factory torque-to-yield head fasteners, the fasteners must be retorqued after the first heat-up/cool-down cycle prior to dyno runs. Failure to do this will most certainly result in a blown head gasket. Retorque requires backing off one fastener in the correct sequence then bringing back to torque. Then the next in sequence, and so on, until all are done on both banks." Also keep in mind that a MID-specific Cometic head gaskets must be used and are available from Darton.

After the three small O-rings were put in place, the sleeve was treated to some Molykote O-ring lube. The O-rings are there to keep coolant from leaking into the crankcase, which is exactly the same method used in wet-sleeve diesel engines.

The next day, Steve stress relieved the block for another half hour before beginning to deck the block. The final deck height ended up coming in at 9.235 inches.

Steve then applied a thin layer of Loctite 515 flange sealant (PN 51531) to the top of the sleeves. This is applied between the sleeves near the deck surface and around the flanges to both prevent leaks and hold the sleeves in place during decking and boring.

The sleeves were then secured in place and allowed to set-up overnight. It's important to keep in mind that the Loctite is there just to seal, and not hold the sleeves in place; that's eventually done by the heads being bolted on. Sleeved blocks (wet or dry) must never be washed in a jet wash without honing plates attached or the sleeves will be lifted out of position due to block expansion and will not reseat themselves. This is true even for aftermarket aluminum blocks. The preferred cleaning method is hand washing prior to assembly with warm soap and water.

Steve was also able to dowel our main caps using this slick jig. He charges $250 for the process, but it's money well spent since it adds stability to the rotating assembly. With this done, we were ready to finish-hone and align-hone the block.

We were then able to bore the block to within honing range. With this sleeve kit, we could have gone as large as 4.200 inches for the finished bore but went for a final bore of 4.185 inches. Combine that bore with a 4.125-inch stroker crank and the result would be an all-aluminum 454 small-block.

With that done, the sleeves could then be slid into the machined block. The sleeves are much stronger than the original block bores. This increase in strength allows the engine to make a lot more power without fear of cracking a cylinder wall. The sleeves are made of exactly the same material as what's used in Darton's Top Fuel and Funny Car sleeves.

Steve was also able to dowel our main caps using this slick jig. He charges $250 for the process, but it's money well spent since it adds stability to the rotating assembly. With this done, we were ready to finish-hone and align-hone the block.

Part II in a series that shows how MTI tops off its stout 427 cubic-inch LS1 shortblock with MTI Stage III Heads. Only at www.gmhightechperformance.com, the official site for GM High-Tech Performance Magazine. » Read More